1. Field of the Invention
This invention relates generally to electronic and computer synthesis of sounds. More particularly, it relates to devices and methods for the synthesis of complex ambient background and foreground impact sounds that sound neither repetitive nor looped.
2. Description of the Related Art
Many computer-implemented games and simulations contain background and foreground sounds that help create a highly realistic environment. These complex sounds are often generated using some version of a wavetable synthesis algorithm. A wavetable is a table of stored sound waves, typically stored in read-only memory on a sound card chip, that are digitized samples of actual recorded sound. Complex sounds are generated by combining and modifying the stored sound waves. One of the primary techniques used by wavetable synthesizers to conserve sample memory space is the looping of sampled sound segments. For example, acoustic string instrument sounds can be modeled as attack and sustain portions, and the sustain portion in particular can be reproduced with a repeated sound sample multiplied by a continually decreasing gain factor. In order to generate and complete instrument sound, only a relatively small sample must be stored.
While wavetable synthesis techniques have proven very successful in generating musical instrument sounds, they are inadequate for synthesizing realistic game sounds, which are typically large-scale sound events made up of collections of smaller, simpler sound events. Examples of game sounds include ambient background sounds such as forest or crowd noises and complex foreground sounds such as car crashes or explosions. With standard wavetable synthesis, background sounds such as crowds sound looped, while complex impact sounds are repetitive, i.e., sound identical each time they occur. Repetitive or looped sounds begin to sound unnatural very quickly, dramatically reducing the realism conveyed by the game. Clearly, there is a need for improved techniques for generating realistic game sounds for computer simulators and games.